Absolute quantum yield measurements of fluorescent proteins using a plasmonic nanocavity

One of the key photophysical properties of fluorescent proteins that is most difficult to measure is the quantum yield. It describes how efficiently a fluorophore converts absorbed light into fluorescence. Its measurement using conventional methods become particularly problematic when it is unknown how many of the proposedly fluorescent molecules of a sample are indeed fluorescent (for example due to incomplete maturation, or the presence of photophysical dark states). Here, we use a plasmonic nanocavity-based method to measure absolute quantum yield values of commonly used fluorescent proteins. The method is calibration-free, does not require knowledge about maturation or potential dark states, and works on minute amounts of sample. The insensitivity of the nanocavity-based method to the presence of non-luminescent species allowed us to measure precisely the quantum yield of photo-switchable proteins in their on-state and to analyze the origin of the residual fluorescence of protein ensembles switched to the dark state

Plasmon-assisted Förster resonance energy transfer at the single-molecule level in the moderate quenching regime

Metallic nanoparticles were shown to affect Förster energy transfer between fluorophore pairs. However, to date, the net plasmonic effect on FRET is still under dispute, with experiments showing efficiency enhancement and reduction. This controversy is due to the challenges involved in the precise positioning of FRET pairs in the near field of a metallic nanostructure, as well as in the accurate characterization of the plasmonic impact on the FRET mechanism. Here, we use the DNA origami technique to place a FRET pair 10 nm away from the surface of gold nanoparticles with sizes ranging from 5 to 20 nm. In this configuration, the fluorophores experience only moderate plasmonic quenching. We use the acceptor bleaching approach to extract the FRET rate constant and efficiency on immobilized single FRET pairs based solely on the donor lifetime. This technique does not require a posteriori correction factors neither a priori knowledge of the acceptor quantum yield, and importantly, it is performed in a single spectral channel. Our results allow us to conclude that, despite the plasmon-assisted Purcell enhancement experienced by donor and acceptor partners, the gold nanoparticles in our samples have a negligible effect on the FRET rate, which in turns yields a reduction of the transfer efficiency

A framework for intelligent policy decision making based on a government data hub

Author ProofThe e-Oman Integration Platform is a data hub that enables data exchanges across government in response to transactions. With millions of transactions weekly, and thereby data exchanges, we propose to investigate the potential of gathering intelligence from these linked sources to help government officials make more informed decisions. A key feature of this data is the richness and accuracy, which increases the value of the learning outcome when augmented by other big and open data sources. We consider a high-level framework within a government context, taking into account issues related to the definition of public policies, data privacy, and the potential benefits to society. A preliminary, qualitative validation of the framework in the context of e-Oman is presented. This paper lays out foundational work into an ongoing research to implement government decision-making based on big data.“SmartEGOV: Harnessing EGOV for Smart Governance (Foundations, Methods, Tools)/NORTE-01-0145-FEDER-000037”, supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (EFDR

Time-resolved x-ray phase-contrast tomography of sedimenting micro-spheres

We have implemented a time-dependent (dynamic) x-ray tomography of sedimenting micro-spheres suspended in water. To achieve phase contrast at high magnification we use the divergent and highly coherent beam emitted from an x-ray waveguide. Holograms are recorded with 5 ms acquisition time while the sample is rotated at 1 Hz, over a run of 40 s. We show that under these conditions, more than 20 000 individual particle trajectories can be tracked. The analysis of the trajectories shows apparent super-diffusive behavior due to collective flow patterns, as also further evidenced by plotting the temporal averaged spatial distribution of particle densities and velocities

Three-dimensional phase retrieval in propagation-based phase-contrast imaging

We present a solution to the phase problem in near-field x-ray (propagation) imaging. The three-dimensionalcomplex-valued index of refraction is reconstructed from a set of projections recorded in the near-field (Fresnel)setting at a single detector distance. The solution is found by an iterative algorithm based only on the measureddata and the three-dimensional tomographic (Helgason-Ludwig) consistency constraint without the need forfurther a priori knowledge or other restrictive assumptions